Can I set the config.php file to read only? If so, how?

[familytreeview]

Message I get shown below but I cannot find how to change the setting on it in the File Management.

"Your config.php file is still writable. For security, you should set the permissions of this file back to read-only when you have finished configuring your site."

[filsil]

You can change the permissions of a file with an FTP client